Insulation of electrical apparatus



Oct. 13, 1931. M. EjFENE l,827571 INSULATION OF ELECTRICAL APPARATUS Filed Oct. 8, 1930 7 Inventor: Marcus E. Fiene,

bg %MM His -Attorneg Patcnted Oct. 13, 1931 i 1,827,571

UNITED s'rA'rEs PATENT OFFICE maus n. rinna, or numron mlm, miw !omg ASSIGNOB 'ro a merma,

conrm. A coaromrow or mw you INBULATION OI' ELECTBICAL APPARATUS v Application med October 8, 1930. Serial No. 487.804.

The .present invention relates to electrical apparatus and is more specifically, concerned with a process for insulating coils for electri'cal purposes and the product produced by such process.

' those suitable as refrigerants, su

A rincipal object of this invention is the a provson of a coil which will havehighly each other so that the wholeis a compact,

15 solid, well insulated unit.

My invention will be more fully set forth in the following description, reference being had to the accompanying drawings,and its scope will be pointed .out in the claims annexed to and forming part of this specification. i

In the drawings, Fi 1 is a erspective View, partially broken or the sa e of clearness, of a stator of a dynamo electric machine the windings thereof being insulated in accordance with my invention; Fig. 2 is a diagrammatic sectional View of an apparatus which maybe employed in carrying out the process of my invention and showing a stator therein and illustrating the first steps in the process; Fig. 3 is an enlarged fragmentary cross section of a portion of the stator illustrating diagrammatically the condition of the windings at the stage in the process cor-` res ndin to Fig. 2; Fig. 4 is a view similar to ig. 2 ut illustrating later ste s in the process Fig. 5 is a view similar to ig. 3 but showing the windings at the stage of the treatment corresponding to Fig. 4; Fig. 6

is a View similar to Fig. 2 but illustrating" the baking operation; and Fig. 7 isa view similar to Fig. 3 but showing the windings as they appear completely insulated by means of the process of the present invention.

- Referring to Fig. 1 of the'drawings, there is shown and generally indicated by the nu meral 1 a stator of a dynamo elejctric machine as representative of an electric al a paratus having a coil .or winding which is nsulated and which may be treated i'n accordance 'with my invention. The stator comprises 'a ma netc body comprising laminations 2 rovied with openings or slots 3 therein. hields 4 composed preferably of non-magnetic metal, such as brass, are rovided in order to protect the insulation, esignated eneraly at 5, surrounding .the end turns of t e win ing. These shields are Secured to the stator by any suitable means, for example by soldering thereto as shown at 6. Non-magnetic metallic wedges 7 are provided in the slots 3 as shown more clearly in Figs. 3, 5 and 7.

e In carrying out the process of my inventon the stator is first wound in the usual manner. I employ *fibrous covered conductors, the conductors being preferably copper and the covering thereon a cellulosic material, such as paper, cotton or other fibrous material or such a. cellulosic material admixed with a substance, such asasbestos fibres. The slot insulation may be of the same material as the covering of the conductors but is not necessarily restricted to such 'material but ma include such materials as mica, lacquers an the like.

The stator having been wound and the end shields fastene'd thereto I then introduce I therein an inert inorganic filling material,

such as silica, preferably of 20-30 mesh.

This may be Conveniently done through openings 8 in the shields. Instead of employing 'silica I may use an other inert filling material, which shoul not` be too fine, as for example lumina, boron nitride, thoria, and the li e. After this inert material has been introduced the holes or o nings 8 are closed in any suitable way, as or exam le by soldering. The stator is now ready or the impregnation steps.

The stator s placed in a suitable recep- -tacle 9 provided with a removable cover 10,

and inlet and outlet pipes, '11 and 12, respectively, for the admission and withdrawal of the impregnating medium or agent, the pipes 11 and' 12 having suitable controlling valves 13 and 14, respectively. The receptacle 9 is also provided with a pipe 15 leadin to a valve mechansm 16 whch is operative y connected to and controls suction andpressure lines 17 and 18 respectively. The stator havbeen placed in the receptacle the latter is closed and the valve 16 manipulated to connect the receptacle with the source of suction. After the receptacle is evacuated the valve 13 is opened to admit the impregnating agent 19 which is introduced until the stator s completely submerged therein (see Fig. 4) The suction supply is now cut ofi. As the impregnating agent I employ a material, such as sodium silicate, potassium silicate, and the like. I prefer to employ sodium silicate because of its general availability and comparative cheapness. It acts as an excellent coating material and sets to a rigid bond. I have found that a sodium silicate solution made from sodium silicate known to thb trade as N brand and having a ratio of Na O to SiO of 1: 3.25 the solution being of specific gravitv of approximately 1.37 gives excellent results, but it is of course understood that my invention is not restricted to the use of this material nor to this particular specific gravity. i

The valve mechanism 16 is now manipulated so that pressure is supplied through the line 18. While the pressure may vary I have found that the application of about pounds pressure for about one hour is satisfactory. If higher pressures are employed the time is decreased. The impregnating agent enters the stator through the slots 3 and impregnates the covered conductors and the inert filling material. Fig. 3 illustrates on an enlarged scale and somewhat diagrammatically the condition of the coil or windings after the inert filling material has been supplied, while Fig. 5 shows similarly the condition of the windings while the stator is being treated as shown in Fig. 4.

After impregnation the stator is removed and placed in a suitable baking oven, such as the electrically heated oven 20 shown in Fig. 6. The oven is arranged so that thestator is heat-treated in an inert environment, that is, the stator receives the heat treatment in an inert gaseous medium or in a vacuum. The importance of this will be pointed out more fully hereafter. The temperature at which the stator is baked is such that the cellulosic material is decomposed and the impregnating agent is caused to firmly set and bind the individual conductors in place and also to bind the inert filling medium. I have found that a baking temperature of about 400 C. is satisfactory, although this temperature is not fixed and may be varied.

During the heat treatmentin the inert atmosphere the cellulosic material surrounding the conductors of the coil decomposes to a stable compound of indeterminate composition but which is an excellent insulator. At the same time that this decomposition takes place the inert filling material is firmly bonded together by the impregnating agent, which also bonds the insulaton covering firmly on the conductors. It is im ortant that the heat treatment be carrie out in the absence of air else the cellulosic material surrounding the conductors will not decompose to the stable product obtained by the process of my invention but will oxidize and in most cases completely burn out. In Fig. 7 I have indicated on an enlarged scale and somewhat diagrammatically the coil or windings insulated after the heat treatment.

The stator is again impregnated and baked as above. The second impregnation improves the mechanical strength of the decomposed cellulosic material surrounding and insulating the individual conductors, the impregnating agent acting also s a bindet. This decomposed cellulosic material also acts as an absorbent for the impregnating agent and prevents intumescence. Further impregnations and baking Operations may be carried out as it is not my intention to restrict the number of impregnations and baking operationsto two, although two such Operations will ordinarily be found suflicient.

In some cases, after the final baking operation has been carried out it may be desirable, though not necessary, to impregnate the coil or winding with a molten inorganic insulating material of fairly high melting point i. e. over about 100 C. but below about 600 C., and which is insoluble or but slightly soluble in water, such as lead borate, lead chloride, sulphur and the like, in order to completely seal any minute pores which may be present.

This is carried out by simply impregnating with the material which is allowed to solidify in air. Such a treatment will further improve the moisture resistance and mechanical qualities of the unit.

A coil for-med and insulated in accordance with my invention is highly refractory in nature, and unafiected by lubricating oils. Such a coil is furthermore resistant to and unafl'ected by certain refrigerants, for example, sulphur dioxide, methyl formate, -methyl chloride and the like, so that the coil is particularly suited for use in any electrical apparatus enclosed in a refrigerating system.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. The process of making and insulating a coil for electrical purposes, said coil consisting of fibrous covered conductors, which includes the steps of filling the spaces between the turns of the conductors with an inert filling material, impregnating with an agent adapted to coat the conductors and bind the filling material, and heating said coil so treated, in an inert environment, to cause the impregnating agent to bond the filling material and conductors in place and to decompose said fibrous covering to a stable insulating product.

2. The process of making and insulating a coil for electrical purposes, said coil consisting of fibrous covered conductors, which includes the stefis of filling the spaces between the turns of t e conductors with an inert inorganic filling material, impregnating with a silicious body adapted to coat the conduc- .tors and bind the filling material, and heat ing the coil in a'n inert environment 'at about 3. The process of making coils for electrical purposes which includes the ste s of filling the spaces between the turns of fi rous covered conductors with silica, impregnating with sodium silicate, heating in an inert atmosphere at about 400 C., and repeatingsaid impregnation and baking operatons.

4. The process of making electrical apparatus having a core structure and an insulated winding which includes the steps of fill- 'ing the spaces between the'windings and the 9 core structure with silica, submerging said structure in a bath of sodium silicate and impregnating the conductors and silica therewith, heating said structure 'in an inert atmosphere at about 400 C., and again impreg nating and heating as set forth. i

5. The process of making and insulating a coil for electrical purposes, said coil consisting of fibrous covered conductors, which includes the steps of filling the spaces between 'the turns of the conductors with silica, im- Eregnating said coil with sodium silicate,

eating said coil in an inert atmosphere at about 400 C., repeating said impregnation' and bakingoperations one or more times, and finally impregnating said coil with a high melting, substantiallyinsoluble inorganic in- I sulating material, and allowing said latter impregnating agent to solidify' in air.

6. An electrical rcoil the' turns of which are seperated by a stable insulating decomposition product of cellulose and an inert inor-' ganic material.

7 An electrical -coil the turns of which are enerated by a composition comprising a cellulosic material heat treated in an inert atmolsphere and bonded with a silicious matera 8. An electrical coil the turns of which are separated bv and insulated with a composition comprising a cellulosic material heat treated in an inert atmosphere and bonded together with sodium silicate. said turns being also separated by and bonded together with a rigid insulation comnrisingan inertinor- ;mnie fillin material bonded with said sodiu-m silica 9. An electrical coil the turns'of which are separated by' and insulated with a `composi- -tion comprising a product produced by heat treatinz a cellulosic material at about 400 C. in an inert atmosphere, said product being bonded with silicate of an alkali metal. i

comprising a product produced by heat treating a cellulosc material at about 400 C. in an inert atmosphere, said winding being also insulated b a-bondin of sodium silicate.

11. An e ectrical col the' turns of which are separated by and insulated with a stable, insulating decompcsition product of cellulosic material and bonded together with so-` 10. An electrical apparatus having a core structure and an insulated wndmg, said s winding being insulted with composition 

